A vehicle display device proposed recently (see, for example, Patent Literature 1) displays an image (vehicle information image) representing vehicle information, such as a vehicle speed and an engine rotation speed, and an image (external image) obtained from an external device at a time on a meter display disposed in front of a driver's seat within an instrument panel of a vehicle.
The external device referred to herein includes various devices, examples of which include but not limited to a navigation device and a smartphone.
An external image is not always displayed on a screen of the meter display. That is to say, a transient period occurs when the screen of the meter display is switched from a state where an external image is not displayed to a state where the external image is displayed.
An external image is newly displayed, for example, when external image data is inputted from the external device from which the external image has not been outputted. A study is now under way on a vehicle display device configured to hide an external image which is relatively less useful than a vehicle information image when a driving load on a driver is determined to be high to let the driver concentrate on a driving operation. According to the configuration as above, the hidden external image is displayed again on the meter display when a driving load on the driver is determined to fall within an allowable range.
In a case where an external image newly displayed by switching the display screens is a bright image in comparison with a vehicle information image, the driver may feel the external image too bright, which raises a problem that visibility of the vehicle information image is reduced.
The driver feels a displayed external image too bright in cases other than transition of an external image from a hidden state to a displayed state. For example, when an external image is switched to a new image different from an image which has been displayed up to present time, the driver may also feel the external image too bright.
That is to say, a bright image is displayed suddenly by switching external images when brightness of an external image displayed after switching is higher than brightness of an external image displayed before switching. Hence, the driver also feels the external image too bright. An external image is switched to an image different from an image which has been displayed up to present time, for example, when a user makes an operation to change the external image on the external device which is outputting the external image.
In order to address the problem that the driver feels an external image too bright when an external image which has not been displayed is displayed due to transition of the external image from a hidden state to a displayed state or transition of screen types as described above, an amount of light of a backlight may be reduced once when the external image is newly displayed. When configured in such a manner, a possibility that the driver feels the external image too bright may be reduced.
However, when an amount of light of the backlight is reduced, brightness of an entire display region of the meter display is decreased and a vehicle information image also becomes dark. After all, visibility of the vehicle information image is reduced.